Various studies have recently been conducted on the use of a film as an innerliner member, the film having a main component of a thermoplastic resin or a thermoplastic elastomer composition containing a blend of a thermoplastic resin and an elastomer, in order to achieve both a reduction in total tire weight and improved high air permeation preventive properties (for example, see Japanese Unexamined Patent Application Publication No. H08-217932A and International Patent Application Publication Nos. WO 2008/53747 and WO 2012/086276).
For example, studies have been conducted on the use of an innerliner member as a tire structural member, the innerliner member being pasted on the tire inner circumferential surface, the innerliner member being constituted from an at least three-layer structure including a film having a main component of a thermoplastic resin or a thermoplastic elastomer composition containing a blend of a thermoplastic resin and an elastomer, and rubber sheets layered on both sides of the film. To use an innerliner member of this type as a tire structural member, a production method is employed wherein the innerliner member is wound around a tire molding drum, the end portions thereof are lap spliced, and the tire is submitted to a vulcanization step (for example, see Japanese Unexamined Patent Application Publication Nos. 2006-198848A and 2012-6499A).
Specifically, there is a technique in which an innerliner member having such a layered structure is wound around a tire molding drum so as to have a cylindrical shape, and at that time the two circumferential direction end portions are lap spliced to each other and then the tire is submitted to a vulcanization molding step to produce a pneumatic tire.
When such a technique is used, it is preferable to use an innerliner member configured from an at least three-layer structure including a film and rubber sheets layered on both sides of the film, because the rubber sheets are overlapped and lap spliced to each other and the two end portions can be securely bonded.
However, during the process from during vulcanization molding to immediately after molding, separation occurs at the interfaces between the film and rubber sheets, and the bond portion (splice portion) opens.
To describe this through drawings, as illustrated in FIG. 4A, an innerliner member 1 constituted of an at least three-layer structure including a film 2, having a main component of a thermoplastic resin or a thermoplastic elastomer composition containing a blend of a thermoplastic resin and an elastomer, and rubber sheets 3A, 3B layered on both sides of the film 2 is formed into a required size (length) determined according to tire size, and a lap splice portion 4 is provided on both end portions thereof on a tire molding drum 5 illustrated schematically by double-dotted lines. The end portions are overlapped and lap sliced to each other so that the innerliner member is formed into a ring as a whole. The rubber sheet 3B functions as tie rubber having a function of bonding with other tire components such as the carcass layer. In FIGS. 4A to 4C, the top is the tire radial direction outer side, the bottom is the tire radial direction inner side, and the lateral direction is the tire circumferential direction.
In the steps from green tire molding to vulcanization molding, the lap splice portion 4 of the innerliner member 1 may incur a separation condition 6 at the interface between the film 2 and rubber sheet 3A as illustrated in FIG. 4B, particularly at the interfaces in the vicinity of the end portions. For example, because the adhesion bonding force (tack) between the surface of the molding drum 5 and the rubber sheet 3A constituting the innerliner member 1 is strong, when the green tire is molded and removed from the molding drum 5, the vicinity of the end portions of the rubber sheet 3A is pulled toward the molding drum 5 side, causing a separation condition 6 at the interface between the film 2 and rubber sheet 3A.
As a whole, the innerliner member after vulcanization molding forms an innerliner layer 10 as illustrated in FIG. 4C. In the vicinity of the lap splice portion 4, the end portions of the film 2 overlap, with members consisting of rubber sheets interposed therebetween. The region surrounded by a dotted line in the tip vicinity 7 of the film 2 of FIG. 4C is a position where attention should be paid to tire failure, such as separation of the film 2 and rubber members during molding of the pneumatic tire and during travel.